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dr_dave
09-03-2008, 12:34 PM
FYI, Bob Jewett and I recently spent a weekend filming demos and performing experiments. Below are the clips we put together. We also might write some articles in the near future concerning some of the details and other results.

NV B.49 - Using your knuckles to prevent a double hit and stop the cue ball, with Bob Jewett (http://billiards.colostate.edu/normal_videos/new/NVB-49.htm)

NV B.50 - Using your knuckles to prevent a double hit and get follow, with Bob Jewett (http://billiards.colostate.edu/normal_videos/new/NVB-50.htm)

NV B.51 - Using your natural forward stroke limit to prevent a double hit and get draw, with Bob Jewett (http://billiards.colostate.edu/normal_videos/new/NVB-51.htm)

NV B.52 - Using a fouette shot to prevent a double hit, with Bob Jewett (http://billiards.colostate.edu/normal_videos/new/NVB-52.htm)

NV B.53 - How to determine which ball was hit first by watching the cue ball, with Bob Jewett (http://billiards.colostate.edu/normal_videos/new/NVB-53.htm)

NV B.54 - How to determine which ball was hit first by watching the object balls, with Bob Jewett (http://billiards.colostate.edu/normal_videos/new/NVB-54.htm)

<a href="http://billiards.colostate.edu/normal_videos/new/NVB-55.htm" target="_blank">NV B.55 - Bob Jewett's two-times-fuller frozen-cue-ball aiming system
</a>
NV B.56 - Bob Jewett's ten-times-fuller frozen-object-ball aiming system (http://billiards.colostate.edu/normal_videos/new/NVB-56.htm)

NV B.57 - Kick shot speed, topspin, and bottom-spin effects, with Bob Jewett (http://billiards.colostate.edu/normal_videos/new/NVB-57.htm)

HSV B.40 - stroke speed and acceleration analysis, with Bob Jewett (http://billiards.colostate.edu/high_speed_videos/new/HSVB-40.htm)

HSV B.41 - bank speed effects, with Bob Jewett (http://billiards.colostate.edu/high_speed_videos/new/HSVB-41.htm)

HSV B.42 - tip and cue efficiency, with Bob Jewett (http://billiards.colostate.edu/high_speed_videos/new/HSVB-42.htm)

We hope you enjoy the clips and find them useful. We also look forward to your comments, questions, and suggestions.

Regards,
Dave

wolfdancer
09-03-2008, 01:11 PM
Once again Dr. Dave thanks for your contributions here.
What a pairing ...Dr.Dave and Bob Jewett...
brains and brawn ? /forums/images/%%GRAEMLIN_URL%%/laugh.gif
These videos, I'm going to really look forward to viewing...Bob is widely respected for both his knowledge and ability, and you shoot a mean camera.... /forums/images/%%GRAEMLIN_URL%%/cool.gif
Seriously, this has all the makings of a great collaboration...
The fouette shot is new to me, and a great tip!!!

av84fun
09-03-2008, 01:13 PM
Great stuff Dave. I will have several questions but first, could you explain what positives/negatives are associated with cue/tip "efficiency?"

I'm going to risk opening mouth and inserting foot by guessing that the more efficient the cue/tip the faster the more energy (momentum?) will be imparted to the CB at a given impact speed.

Please correct me if I'm wrong and also mention what negatives might be associated with that effeciency....for example, is there less tip/CB contact time and therefore, less spin and/or deflection?

THANKS!

Jim

dr_dave
09-03-2008, 02:10 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">Great stuff Dave. I will have several questions but first, could you explain what positives/negatives are associated with cue/tip "efficiency?"

I'm going to risk opening mouth and inserting foot by guessing that the more efficient the cue/tip the faster the more energy (momentum?) will be imparted to the CB at a given impact speed.</div></div>That's correct. A phenolic tip delivers more energy/momentum/speed to the cue ball.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">Please correct me if I'm wrong and also mention what negatives might be associated with that effeciency....for example, is there less tip/CB contact time and therefore, less spin and/or deflection?</div></div>The phenolic tips do have less contact time, and this should theoretically result in less squirt than with a leather tip, but we did not test this (but I wouldn't expect this to be a large effect). There is no argument for less spin though (see the 2nd Q&A here (http://billiards.colostate.edu/threads/cue.html#low_squirt)); although, phenolic tips aren't good for lots of spin anyway.

Regards,
Dave

skin
09-03-2008, 03:45 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">Great stuff Dave. I will have several questions but first, could you explain what positives/negatives are associated with cue/tip "efficiency?"

I'm going to risk opening mouth and inserting foot by guessing that the more efficient the cue/tip the faster the more energy (momentum?) will be imparted to the CB at a given impact speed.</div></div>That's correct. A phenolic tip delivers more energy/momentum/speed to the cue ball.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">Please correct me if I'm wrong and also mention what negatives might be associated with that effeciency....for example, is there less tip/CB contact time and therefore, less spin and/or deflection?</div></div>The phenolic tips do have less contact time, and this should theoretically result in less squirt than with a leather tip, but we did not test this (but I wouldn't expect this to be a large effect). There is no argument for less spin though (see the 2nd Q&A here (http://billiards.colostate.edu/threads/cue.html#low_squirt)); although, phenolic tips aren't good for lots of spin anyway.

Regards,
Dave </div></div>

Dave, how can you separate the efficiencies of the tips from the eficiencies of the cues? Wouldn't you need to compare tips on the same cue to isolate tip efficiency and vice versa for cue efficiency? Just wondering is all. Thanks in advance for your reply.

-skin

dr_dave
09-03-2008, 03:51 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: skin</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">Great stuff Dave. I will have several questions but first, could you explain what positives/negatives are associated with cue/tip "efficiency?"

I'm going to risk opening mouth and inserting foot by guessing that the more efficient the cue/tip the faster the more energy (momentum?) will be imparted to the CB at a given impact speed.</div></div>That's correct. A phenolic tip delivers more energy/momentum/speed to the cue ball.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">Please correct me if I'm wrong and also mention what negatives might be associated with that effeciency....for example, is there less tip/CB contact time and therefore, less spin and/or deflection?</div></div>The phenolic tips do have less contact time, and this should theoretically result in less squirt than with a leather tip, but we did not test this (but I wouldn't expect this to be a large effect). There is no argument for less spin though (see the 2nd Q&A here (http://billiards.colostate.edu/threads/cue.html#low_squirt)); although, phenolic tips aren't good for lots of spin anyway.

Regards,
Dave </div></div>

Dave, how can you separate the efficiencies of the tips from the eficiencies of the cues since you used different cues in the tests? Wouldn't you need to compare tips on the same cue to isolate tip efficiency? Just wondering is all. Thanks in advance for your reply.

-skin </div></div>That's a good point. All we showed is that the jump and break cues with phenolic tips we tested all had better efficiency than all of the playing cues with leather tips.

Regards,
Dave

Bob_Jewett
09-03-2008, 08:18 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: skin</div><div class="ubbcode-body"> ... how can you separate the efficiencies of the tips from the efficiencies of the cues? Wouldn't you need to compare tips on the same cue to isolate tip efficiency and vice versa for cue efficiency? ... </div></div>
I'd have to check my hunch, but I believe that the main contribution to inefficiency can only come from the part of the cue that compresses the most. For a leather-tipped cue, I'm pretty sure that is the tip. The reason for this is that loss of energy only appears on the "recovery" phase of the hit when whatever has compressed expands back out releasing energy. While the wood of the cue does some of this, I think it is much smaller than the compression of the tip. I did a simulation that shows how much each compresses, but I can't get to it right now.

cushioncrawler
09-03-2008, 11:56 PM
Bob -- I reckon that contribution to e might be more complicated. Perhaps some more e combinations might be worthwhile. The guilty partyz are, the anvil, the ball, the tip, the cue, air.

I am thinking that if u bounced a ball off a leather tip stuck direktly on that anvil it might suggest that e = say 0.88.
A ball bouncing off the nude anvil might giv e = 0.96.
A cue without tip bouncing off the nude anvil might giv e = 0.82.
Cue with leather tip woz (your) 0.73 (if i remember awright).
And i am wondering whether e for ball/cue might be significantly different to e for anvil/cue. madMac.

wolfdancer
09-04-2008, 01:54 AM
Mac, you're off your meds again? Do you think Efran knows, or even cares about that stuff.

skin
09-04-2008, 07:36 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bob_Jewett</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: skin</div><div class="ubbcode-body"> ... how can you separate the efficiencies of the tips from the efficiencies of the cues? Wouldn't you need to compare tips on the same cue to isolate tip efficiency and vice versa for cue efficiency? ... </div></div>
I'd have to check my hunch, but I believe that the main contribution to inefficiency can only come from the part of the cue that compresses the most. For a leather-tipped cue, I'm pretty sure that is the tip. The reason for this is that loss of energy only appears on the "recovery" phase of the hit when whatever has compressed expands back out releasing energy. While the wood of the cue does some of this, I think it is much smaller than the compression of the tip. I did a simulation that shows how much each compresses, but I can't get to it right now. </div></div>

Bob, it looks to me from the video that some of those cue shafts do not have a full recovery (bend then fully unbend) before lift off and that is why you see the shafts shivering as the cue is in the air. That has to represent inefficency in the cue and not the tip, doesn't it, because it is the shaft and not the tip that is releasing energy perpendicular to the line of force? I'm not an engineer, so I might be thinking the wrong way about this.

But, it is interesting stuff you guys did.

-skin

dr_dave
09-04-2008, 01:42 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wolfdancer</div><div class="ubbcode-body">What a pairing ...Dr.Dave and Bob Jewett...
brains and brawn ? /forums/images/%%GRAEMLIN_URL%%/laugh.gif</div></div>Bob is quite the knuckle-smashing brute in the videos. I see what you mean. /forums/images/%%GRAEMLIN_URL%%/grin.gif

dr_dave
09-04-2008, 01:53 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: skin</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bob_Jewett</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: skin</div><div class="ubbcode-body"> ... how can you separate the efficiencies of the tips from the efficiencies of the cues? Wouldn't you need to compare tips on the same cue to isolate tip efficiency and vice versa for cue efficiency? ... </div></div>
I'd have to check my hunch, but I believe that the main contribution to inefficiency can only come from the part of the cue that compresses the most. For a leather-tipped cue, I'm pretty sure that is the tip. The reason for this is that loss of energy only appears on the "recovery" phase of the hit when whatever has compressed expands back out releasing energy. While the wood of the cue does some of this, I think it is much smaller than the compression of the tip. I did a simulation that shows how much each compresses, but I can't get to it right now. </div></div>

Bob, it looks to me from the video that some of those cue shafts do not have a full recovery (bend then fully unbend) before lift off and that is why you see the shafts shivering as the cue is in the air. That has to represent inefficency in the cue and not the tip, doesn't it, because it is the shaft and not the tip that is releasing energy perpendicular to the line of force? I'm not an engineer, so I might be thinking the wrong way about this.

But, it is interesting stuff you guys did.

-skin </div></div>Impact inefficiency (energy loss) between the cue and the cue ball has several sources, for example:

- tip compression hysteresis and damping
- acoustic waves in the air (the sound you hear)
- cue longitudinal (axial) shockwaves
- cue transverse vibrations (as you mention above)

I agree with Bob's hunch that tip losses are the primary factor in the tests we ran.

Regards,
Dave

av84fun
09-04-2008, 04:40 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: skin</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bob_Jewett</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: skin</div><div class="ubbcode-body"> ... how can you separate the efficiencies of the tips from the efficiencies of the cues? Wouldn't you need to compare tips on the same cue to isolate tip efficiency and vice versa for cue efficiency? ... </div></div>
I'd have to check my hunch, but I believe that the main contribution to inefficiency can only come from the part of the cue that compresses the most. For a leather-tipped cue, I'm pretty sure that is the tip. The reason for this is that loss of energy only appears on the "recovery" phase of the hit when whatever has compressed expands back out releasing energy. While the wood of the cue does some of this, I think it is much smaller than the compression of the tip. I did a simulation that shows how much each compresses, but I can't get to it right now. </div></div>

Bob, it looks to me from the video that some of those cue shafts do not have a full recovery (bend then fully unbend) before lift off and that is why you see the shafts shivering as the cue is in the air. That has to represent inefficency in the cue and not the tip, doesn't it, because it is the shaft and not the tip that is releasing energy perpendicular to the line of force? I'm not an engineer, so I might be thinking the wrong way about this.

But, it is interesting stuff you guys did.

-skin </div></div>Impact inefficiency (energy loss) between the cue and the cue ball has several sources, for example:

- <span style='font-size: 14pt'>tip compression hysteresis and damping</span>- acoustic waves in the air (the sound you hear)
- cue longitudinal (axial) shockwaves
- cue transverse vibrations (as you mention above)

I agree with Bob's hunch that tip losses are the primary factor in the tests we ran.

Regards,
Dave </div></div>

Do tips also suffer from depression and hysteria????

(-:

Jim

cushioncrawler
09-04-2008, 05:14 PM
Bob'n'Dave -- I go along with what u say that the drop tests merely show the difference tween som tips and cues. But i still hav som thorts.

How about testing bakelite tips on the ordinary cues??
How about testing leather tips on the break and jump cues??
This might tell u/us about a tip's contribution.

And, re Skins'z thorts -- i think that shaft vibration etc might be a giant factor at real break etc speedz -- which reminded me that the drop tests were at perhaps only 1/5th real speedz.

And dont tell Woofly that i am now uzing the world'z longest cue, i mean in matchplay (and in all my play) -- 23.5oz, and 12" longer than a "standard" 56" billiard/snooker cue -- and, it haz zero ferrule. madmac.

skin
09-04-2008, 10:27 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: skin</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bob_Jewett</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: skin</div><div class="ubbcode-body"> ... how can you separate the efficiencies of the tips from the efficiencies of the cues? Wouldn't you need to compare tips on the same cue to isolate tip efficiency and vice versa for cue efficiency? ... </div></div>
I'd have to check my hunch, but I believe that the main contribution to inefficiency can only come from the part of the cue that compresses the most. For a leather-tipped cue, I'm pretty sure that is the tip. The reason for this is that loss of energy only appears on the "recovery" phase of the hit when whatever has compressed expands back out releasing energy. While the wood of the cue does some of this, I think it is much smaller than the compression of the tip. I did a simulation that shows how much each compresses, but I can't get to it right now. </div></div>

Bob, it looks to me from the video that some of those cue shafts do not have a full recovery (bend then fully unbend) before lift off and that is why you see the shafts shivering as the cue is in the air. That has to represent inefficency in the cue and not the tip, doesn't it, because it is the shaft and not the tip that is releasing energy perpendicular to the line of force? I'm not an engineer, so I might be thinking the wrong way about this.

But, it is interesting stuff you guys did.

-skin </div></div>Impact inefficiency (energy loss) between the cue and the cue ball has several sources, for example:

- tip compression hysteresis and damping
- acoustic waves in the air (the sound you hear)
- cue longitudinal (axial) shockwaves
- cue transverse vibrations (as you mention above)

I agree with Bob's hunch that tip losses are the primary factor in the tests we ran.

Regards,
Dave </div></div>

Thanks for that technical explanation, Dave. It is meat that the teeth can be sunk into.

I realize you guys weren't doing a comprehensive analysis of all those factors. But, it would be very interesting to see them subjected to systematic high speed video analysis where possible since almost all of it is beyond what the naked senses can pick up.

-skin

Qtec
09-05-2008, 07:46 AM
IMO to demonstrate a pendelum motion the shoulder has to be much lower than you or Bob demonstrated. In both your videos, the cue came back almost level, when with a P stroke, the cue would come back higher on the backstroke. In a P motion only the forearm should be moving and the upper arm muscles are passive.

Just an observation.

Q

dr_dave
09-05-2008, 08:52 AM
Mac,

Thanks for the ideas. If we ever reassemble the tester and get somebody to help with the tip changing, we will perform the additional tests.

Concerning the energy lost into shaft vibrations, I still think it will be much lower than the energy lost due to tip inelasticity. Hopefully, we (or you) can test this more thoroughly in the future.

Regards,
Dave

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cushioncrawler</div><div class="ubbcode-body">Bob'n'Dave -- I go along with what u say that the drop tests merely show the difference tween som tips and cues. But i still hav som thorts.

How about testing bakelite tips on the ordinary cues??
How about testing leather tips on the break and jump cues??
This might tell u/us about a tip's contribution.

And, re Skins'z thorts -- i think that shaft vibration etc might be a giant factor at real break etc speedz -- which reminded me that the drop tests were at perhaps only 1/5th real speedz.

And dont tell Woofly that i am now uzing the world'z longest cue, i mean in matchplay (and in all my play) -- 23.5oz, and 12" longer than a "standard" 56" billiard/snooker cue -- and, it haz zero ferrule. madmac.

</div></div>

Eric.
09-05-2008, 09:17 AM
Good stuff, guys.

The frozen ball system was always interesting. One thing I always found, the balls ABSOLUTELY ahve to be frozen (not even a hair of space) for this to work. Otherwise, nice arrow for the quiver.

Eric

dr_dave
09-05-2008, 09:58 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Eric.</div><div class="ubbcode-body">Good stuff, guys.

The frozen ball system was always interesting. One thing I always found, the balls ABSOLUTELY ahve to be frozen (not even a hair of space) for this to work. Otherwise, nice arrow for the quiver.

Eric </div></div>Excellent point. I think Bob stresses this in at least one of the videos.

Regards,
Dave

dr_dave
09-05-2008, 10:03 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body">...
Impact inefficiency (energy loss) between the cue and the cue ball has several sources, for example:

- <span style='font-size: 14pt'>tip compression hysteresis and damping</span>- acoustic waves in the air (the sound you hear)
- cue longitudinal (axial) shockwaves
- cue transverse vibrations (as you mention above)
...</div></div>Do tips also suffer from depression and hysteria????
(-:

Jim </div></div>Very funny. /forums/images/%%GRAEMLIN_URL%%/smirk.gif

Sorry for the fancy words. Hysteresis refers to the difference between the tip compression force over time and the rebound force over time (which is less). Damping refers to energy loss within the tip material as heat resulting from friction and non-ideal material properties.

Regards,
Dave

dr_dave
09-05-2008, 10:11 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Qtec</div><div class="ubbcode-body">IMO to demonstrate a pendelum motion the shoulder has to be much lower than you or Bob demonstrated. In both your videos, the cue came back almost level, when with a P stroke, the cue would come back higher on the backstroke. In a P motion only the forearm should be moving and the upper arm muscles are passive.

Just an observation.

Q </div></div>I'm not sure I totally understand you statement. If the elbow is stationary, why should the shoulder position matter? Also, the cue butt would come up more on the backstroke with a longer bridge (and stroke) length, regardless of the shoulder position, right? I think my cue comes up more than Bob's in the video because I am using more speed and a longer stroke. Neither of us drop our elbow much on the follow-through, so the follow through distance is too short to see significant cue motion (butt up and tip down), but there is some.

Regards,
Dave

av84fun
09-05-2008, 05:43 PM
Your bank speed video was especially interesting to those, like me, who enjoy myth-busting!

But the comment was something to the effect that speed does not always shorten the bank. You certainly proved that to be true but could you comment on what type of shot <u>can</u> be expected to shorten the angle?

To take a wild guess on my own...could it be that since many players use a little outside "helping english" on banks that what happens is that...due to using a hard and likely less accurate stroke, the player imparts more outside than planned thereby getting more squirt...thereby striking the OB more full...thereby shortening the bank???

THANKS!

Jim

cushioncrawler
09-05-2008, 07:37 PM
Dr Dave -- I will do some tests one day -- but theze tests will probably be just for snooker cue(s) and leather tips (and zero tip perhaps). My apparatus will be a ball swinging on 2 cotton strings (at 60dg to each other) hitting the end of a stationary cue. I will mezure the ball'z drop ht and (best) rebound ht -- and somehow equate this to giv "e" etc for the cue hitting a stationary ball.

I think that a leather tip duz some good work that it iznt given credit for -- by softening the blow it must reduce the amount of left-over (wasted) vibration in the shaft -- and by lengthening the impakt time it must again reduce such wastage even moreso. In other words, there will allways be leftover vibrations, but "softer" and "longer" allows more transference, less wastage. Thusly, the heat gain in a leather tip haz a (small) plus side (perhaps moreso for some cues). madMac.<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body">Mac,Thanks for the ideas. If we ever reassemble the tester and get somebody to help with the tip changing, we will perform the additional tests. Concerning the energy lost into shaft vibrations, I still think it will be much lower than the energy lost due to tip inelasticity. Hopefully, we (or you) can test this more thoroughly in the future. Regards,Dave<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cushioncrawler</div><div class="ubbcode-body">Bob'n'Dave -- I go along with what u say that the drop tests merely show the difference tween som tips and cues. But i still hav som thorts. How about testing bakelite tips on the ordinary cues?? How about testing leather tips on the break and jump cues?? This might tell u/us about a tip's contribution.... which reminded me that the drop tests were at perhaps only 1/5th real speedz.... madmac.</div></div></div></div>

skin
09-05-2008, 09:27 PM
"If we ever reassemble the tester and <u>get somebody to help with the tip changing</u>, we will perform the additional tests." -dr_dave

Dave, isn't that why God created graduate students? /forums/images/%%GRAEMLIN_URL%%/grin.gif

-skin

dr_dave
09-06-2008, 10:22 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">Your bank speed video was especially interesting to those, like me, who enjoy myth-busting!

But the comment was something to the effect that speed does not always shorten the bank. You certainly proved that to be true but could you comment on what type of shot <u>can</u> be expected to shorten the angle?</div></div>I have lots of info and video links here:

Let me know if you think something is missing.

Regards,
Dave

dr_dave
09-06-2008, 10:24 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: skin</div><div class="ubbcode-body">"If we ever reassemble the tester and <u>get somebody to help with the tip changing</u>, we will perform the additional tests." -dr_dave

Dave, isn't that why God created graduate students? /forums/images/%%GRAEMLIN_URL%%/grin.gif

-skin </div></div>That would be a good idea if I had money to support a grad student for pool projects and if I could find a grad student that was a good cue and tip craftsman.

Regards,
Dave

av84fun
09-06-2008, 11:53 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">Your bank speed video was especially interesting to those, like me, who enjoy myth-busting!

But the comment was something to the effect that speed does not always shorten the bank. You certainly proved that to be true but could you comment on what type of shot <u>can</u> be expected to shorten the angle?</div></div>I have lots of info and video links here:

Let me know if you think something is missing.

Regards,
Dave </div></div>

Dave, there is a LOT of information at that link. I am on a mission to read and watch everything you do so I WILL get to it all.

In the meantime let me just offer the following which I PROMISE is intended constructively.

It seems to me that NV 6.6 and HSV B.41...in and of themselves and without reference to your other materials are directly contradictory.

NV 6.6, in and of itself stands for the proposition that speed shortens the angle while HSV B.41 shows the opposite.

In B.41 it seems to me, is somewhat artificial due to the intervening OB which I THINK would reduce transferred spin from the CB (which is minor to begin with) to nearly nil.

I suppose that if the frozen ball were removed and the CB struck with perfect centeral ball, then the behavior of the OB off the rail would be the same as with the frozen ball.

In NV 6.6 you seemed to have struck the CB on its vertical center and therefore, it should behave as B 41 but it didn't leaving those, like me, with average intelligence somewhat confused.

I am confident that all will be revealed as I drill deeper into your related materials. Just giving some constructive "user feedback" with respect to the videos viewed alone.

Regards,
Jim

dr_dave
09-08-2008, 04:01 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">It seems to me that NV 6.6 (http://billiards.colostate.edu/normal_videos/NV6-6.htm) and HSV B.41 (http://billiards.colostate.edu/high_speed_videos/new/HSVB-41.htm)...in and of themselves and without reference to your other materials are directly contradictory.</div></div>Agreed. If taken out of context, NV 6.6 (http://billiards.colostate.edu/normal_videos/NV6-6.htm) can be misinterpreted.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">NV 6.6, in and of itself stands for the proposition that speed shortens the angle while HSV B.41 shows the opposite.</div></div>Faster speed does have the effect of shortening the angle with most bank shots (as in NV 6.6 (http://billiards.colostate.edu/normal_videos/NV6-6.htm)). The reason is: the object ball picks up less forward roll than with a slower speed shot, where the object ball (with enough distance) develops complete forward roll before reaching the cushion. With less top spin at cushion impact, the ball doesn't go as long after rebound.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">In B.41 it seems to me, is somewhat artificial due to the intervening OB which I THINK would reduce transferred spin from the CB (which is minor to begin with) to nearly nil.</div></div>The whole point of the "intervening OB" and proximity to the rail was to isolate speed as the only significant factor. The OB hitting the rail has no top, bottom, or side spin, so speed changes are the only real factor in HSV B.41 (http://billiards.colostate.edu/high_speed_videos/new/HSVB-41.htm).

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">I suppose that if the frozen ball were removed and the CB struck with perfect centeral ball, then the behavior of the OB off the rail would be the same as with the frozen ball.</div></div>Correct. If a kicked CB were to arrive at the cushion with stun (no top or bottom spin) and no side spin, it would respond exactly as the banked OB in HSV B.41 (http://billiards.colostate.edu/high_speed_videos/new/HSVB-41.htm).

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">In NV 6.6 you seemed to have struck the CB on its vertical center and therefore, it should behave as B 41 but it didn't leaving those, like me, with average intelligence somewhat confused.</div></div> NV 6.6 (http://billiards.colostate.edu/normal_videos/NV6-6.htm) and NV 6.7 (http://billiards.colostate.edu/normal_videos/NV6-7.htm) demonstrate how changing speed changes the amount of topspin the OB develops before reaching the cushion. The amount of topspin is what dictates how short or long the banked ball goes. In HSV B.41 (http://billiards.colostate.edu/high_speed_videos/new/HSVB-41.htm), the banked ball is stunned into the cushion with no spin whatsoever.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">I am confident that all will be revealed as I drill deeper into your related materials. Just giving some constructive "user feedback" with respect to the videos viewed alone.</div></div>Jim,

Thanks for the feedback. Many of my videos support material in my book and/or articles. The videos were not all designed to be stand-alone. Because of this, some of them can be "taken out of context" (unless you are reading along in the book).

Regards,
Dave

av84fun
09-08-2008, 06:41 PM
THANKS for your thorough explanations. I actaully think I understand....so, now I guess the world can come to and end!!

(-:

Regards,
Jim

dr_dave
09-09-2008, 08:26 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body">THANKS for your thorough explanations. I actaully think I understand....so, now I guess the world can come to and end!!

(-:

Regards,
Jim </div></div>You're welcome. I'm glad the world can come to an end now. /forums/images/%%GRAEMLIN_URL%%/cool.gif

Regards,
Dave

Deeman3
09-09-2008, 08:43 AM
Dave,

How you doing Buddy? I have always thought, that along with the fact a ball struck with speed had little or no forward spin closing the angle, the harshness of the impact of a ball with speed, to a lessor extent, allowed the cushion to "gather" in front of the ball, reducing the rebound angle even further. Is this true? I know the lack of forward rotation has much more effect but am I correct about this?

dr_dave
09-09-2008, 10:25 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Deeman3</div><div class="ubbcode-body">Dave,

How you doing Buddy?</div></div>I'm doing mighty fine; although, with all of these students running around, I can't do as much pool stuff as I did over the summer. /forums/images/%%GRAEMLIN_URL%%/frown.gif

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Deeman3</div><div class="ubbcode-body">I have always thought, that along with the fact a ball struck with speed had little or no forward spin closing the angle, the harshness of the impact of a ball with speed, to a lessor extent, allowed the cushion to "gather" in front of the ball, reducing the rebound angle even further. Is this true? I know the lack of forward rotation has much more effect but am I correct about this? </div></div>Bob and I hope to do a lot more experiments on kick and bank effects in the future. I also hope to try to model all of the physics effects, but I know this will be a very difficult job. There are many physical effects that control the immediate rebound angle and the amount of masse curving after rebound. I use the phrase "rail throwback" to refer to the effect you are describing. With more speed the cushion deforms more and can generate more sideways force to shorten the angle. However, the rebound angle is also affected by the efficiency (coeficient of restitution = COR) of the cushion, and this can vary with speed and angle also. Based on the results in HSV B.41 (http://billiards.colostate.edu/high_speed_videos/new/HSVB-41.htm), I think these two effects are balancing each other out. The rail throwback effect tries to shorten the rebound angle and the efficiency effect apparently tries to lengthen the rebound (because the cushion is returning less energy, maybe partly because of the ball shift down the rail). This is all conjecture, but I think it makes sense physically. I have been interested in investigating this stuff for a long time, but I want to do all of the experiments first.

Regards,
Dave

Deeman3
09-09-2008, 12:27 PM
Dave,

Thanks! You know me. I'd rather just try to think it out and let you scientists do all the hard work and prove the theory....or not. /forums/images/%%GRAEMLIN_URL%%/smile.gif

I have not been hitting them near as much as I'd like either. DeeWoman has a new scoot and keeps draggin me away from tournaments every weekend. /forums/images/%%GRAEMLIN_URL%%/frown.gif

dr_dave
09-09-2008, 12:34 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Deeman3</div><div class="ubbcode-body">Dave,

Thanks!</div></div>You're welcome.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Deeman3</div><div class="ubbcode-body">You know me. I'd rather just try to think it out and let you scientists do all the hard work and prove the theory....or not. /forums/images/%%GRAEMLIN_URL%%/smile.gif</div></div>I'm actually the same way. That's why I've avoided (and continue to avoid) this topic on my "to-do list" for many, many years. In this example, the science is very interesting, but it probably won't contribute much to useful, practical knowledge.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Deeman3</div><div class="ubbcode-body">I have not been hitting them near as much as I'd like either. DeeWoman has a new scoot and keeps draggin me away from tournaments every weekend. /forums/images/%%GRAEMLIN_URL%%/frown.gif </div></div>It sounds like you have your priorities straight ... or not. /forums/images/%%GRAEMLIN_URL%%/wink.gif

Regards,
Dave

cushioncrawler
09-09-2008, 04:14 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Deeman3</div><div class="ubbcode-body">Dave, How you doing Buddy?</div></div>I'm doing mighty fine; although, with all of these students running around, I can't do as much pool stuff as I did over the summer. /forums/images/%%GRAEMLIN_URL%%/frown.gif <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Deeman3</div><div class="ubbcode-body">I have always thought, that along with the fact a ball struck with speed had little or no forward spin closing the angle, the harshness of the impact of a ball with speed, to a lessor extent, allowed the cushion to "gather" in front of the ball, reducing the rebound angle even further. Is this true? I know the lack of forward rotation has much more effect but am I correct about this? </div></div>Bob and I hope to do a lot more experiments on kick and bank effects in the future. I also hope to try to model all of the physics effects, but I know this will be a very difficult job. There are many physical effects that control the immediate rebound angle and the amount of masse curving after rebound. I use the phrase "rail throwback" to refer to the effect you are describing. With more speed the cushion deforms more and can generate more sideways force to shorten the angle. However, the rebound angle is also affected by the efficiency (coeficient of restitution = COR) of the cushion, and this can vary with speed and angle also. Based on the results in HSV B.41 (http://billiards.colostate.edu/high_speed_videos/new/HSVB-41.htm), I think these two effects are balancing each other out. The rail throwback effect tries to shorten the rebound angle and the efficiency effect apparently tries to lengthen the rebound (because the cushion is returning less energy, maybe partly because of the ball shift down the rail). This is all conjecture, but I think it makes sense physically. I have been interested in investigating this stuff for a long time, but I want to do all of the experiments first. Regards, Dave</div></div>Dr Dave -- Dont go there -- Its impossible -- Insanity lurks there -- It kood be your Requiem (like for Mozart??).

Slo-mo's of ballz rebounding from pool cushionz are terryfying. The cushion rubber bendz up, then it kumz down again az it spits the ball back out -- how can one uze Newton for spitting???

And web articles on Tangential Coefficient of Restitution etc miss by a mile. But i hav som thorts on TCOR that i can share if u head down that track. madMac.

wolfdancer
09-09-2008, 05:36 PM
Dr Dave -- Dont go there -- Its impossible -- Insanity lurks there -- /forums/images/%%GRAEMLIN_URL%%/grin.gif
Too late with your warning, Mac /forums/images/%%GRAEMLIN_URL%%/wink.gif

dr_dave
09-10-2008, 10:03 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cushioncrawler</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body">Bob and I hope to do a lot more experiments on kick and bank effects in the future. I also hope to try to model all of the physics effects, but I know this will be a very difficult job. There are many physical effects that control the immediate rebound angle and the amount of masse curving after rebound. I use the phrase "rail throwback" to refer to the effect you are describing. With more speed the cushion deforms more and can generate more sideways force to shorten the angle. However, the rebound angle is also affected by the efficiency (coeficient of restitution = COR) of the cushion, and this can vary with speed and angle also. Based on the results in HSV B.41 (http://billiards.colostate.edu/high_speed_videos/new/HSVB-41.htm), I think these two effects are balancing each other out. The rail throwback effect tries to shorten the rebound angle and the efficiency effect apparently tries to lengthen the rebound (because the cushion is returning less energy, maybe partly because of the ball shift down the rail). This is all conjecture, but I think it makes sense physically. I have been interested in investigating this stuff for a long time, but I want to do all of the experiments first. Regards, Dave</div></div>Dr Dave -- Dont go there -- Its impossible -- Insanity lurks there -- It kood be your Requiem (like for Mozart??).

Slo-mo's of ballz rebounding from pool cushionz are terryfying. The cushion rubber bendz up, then it kumz down again az it spits the ball back out -- how can one uze Newton for spitting???

And web articles on Tangential Coefficient of Restitution etc miss by a mile. But i hav som thorts on TCOR that i can share if u head down that track. madMac. </div></div>Mac,

Thanks for the warnings. I think Newtonian spitting might be an interesting challenge. /forums/images/%%GRAEMLIN_URL%%/wink.gif

Also, separating friction effects from rail throwback (tangential COR), and modeling the speed effects, will be even greater challenges.

That's why I wouldn't even dare attempting physics-based modeling without doing exhaustive empirical (experimental) work first.

Regards,
Dave

dr_dave
09-10-2008, 10:05 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wolfdancer</div><div class="ubbcode-body">Dr Dave -- Dont go there -- Its impossible -- Insanity lurks there -- /forums/images/%%GRAEMLIN_URL%%/grin.gif
Too late with your warning, Mac /forums/images/%%GRAEMLIN_URL%%/wink.gif </div></div>Insanity is good for the soul. You can quote me on that. /forums/images/%%GRAEMLIN_URL%%/sick.gif

Dave

av84fun
09-10-2008, 11:06 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wolfdancer</div><div class="ubbcode-body">Dr Dave -- Dont go there -- Its impossible -- Insanity lurks there -- /forums/images/%%GRAEMLIN_URL%%/grin.gif
Too late with your warning, Mac /forums/images/%%GRAEMLIN_URL%%/wink.gif </div></div>Insanity is good for the soul. <span style='font-size: 14pt'>You can quote me on that.</span> /forums/images/%%GRAEMLIN_URL%%/sick.gif

Dave </div></div>

<span style='font-size: 14pt'>" </span> Insanity is good for the soul. <span style='font-size: 14pt'>"</span>

There ya go. (-:

dr_dave
09-10-2008, 11:53 AM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: av84fun</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wolfdancer</div><div class="ubbcode-body">Dr Dave -- Dont go there -- Its impossible -- Insanity lurks there -- /forums/images/%%GRAEMLIN_URL%%/grin.gif
Too late with your warning, Mac /forums/images/%%GRAEMLIN_URL%%/wink.gif </div></div>Insanity is good for the soul. <span style='font-size: 14pt'>You can quote me on that.</span> /forums/images/%%GRAEMLIN_URL%%/sick.gif

Dave </div></div>

<span style='font-size: 14pt'>" </span> Insanity is good for the soul. <span style='font-size: 14pt'>"</span>

There ya go. (-: </div></div>Thank you. I feel famous now. /forums/images/%%GRAEMLIN_URL%%/blush.gif

Dave

wolfdancer
09-10-2008, 02:44 PM
of course he meant to say ...that way madness lies; let me shun that; no more of that.
But look at the bright side....imagine if it was golf and not pool that piqued your interest /forums/images/%%GRAEMLIN_URL%%/crazy.gif

Deeman3
09-10-2008, 03:16 PM
Dave,

As being one to give you grief early on, I have to say, I have found your book to be very valuable as a reference and much more than I even first gave you credit for in early reading. The added ability to use the on-line references just makes it all the better.

I think hard won praise is more valuable anyway. /forums/images/%%GRAEMLIN_URL%%/smile.gif Keep up the great work.

dr_dave
09-10-2008, 03:54 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Deeman3</div><div class="ubbcode-body">Dave,

As being one to give you grief early on, I have to say, I have found your book to be very valuable as a reference and much more than I even first gave you credit for in early reading. The added ability to use the on-line references just makes it all the better.

I think hard won praise is more valuable anyway. /forums/images/%%GRAEMLIN_URL%%/smile.gif Keep up the great work. </div></div>Dee,

Thank you so much. That means a lot coming from you. I don't mean this in a bad way. I just respect your opinion, which I know is always honest, informed, and practical.

Thanks again,
Dave

cushioncrawler
09-10-2008, 05:05 PM
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cushioncrawler</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body">Bob and I hope to do a lot more experiments on kick and bank effects in the future. I also hope to try to model all of the physics effects, but I know this will be a very difficult job. There are many physical effects that control the immediate rebound angle and the amount of masse curving after rebound. I use the phrase "rail throwback" to refer to the effect you are describing. With more speed the cushion deforms more and can generate more sideways force to shorten the angle. However, the rebound angle is also affected by the efficiency (coeficient of restitution = COR) of the cushion, and this can vary with speed and angle also. Based on the results in HSV B.41 (http://billiards.colostate.edu/high_speed_videos/new/HSVB-41.htm), I think these two effects are balancing each other out. The rail throwback effect tries to shorten the rebound angle and the efficiency effect apparently tries to lengthen the rebound (because the cushion is returning less energy, maybe partly because of the ball shift down the rail). This is all conjecture, but I think it makes sense physically. I have been interested in investigating this stuff for a long time, but I want to do all of the experiments first. Regards, Dave</div></div>Dr Dave -- Dont go there -- Its impossible -- Insanity lurks there -- It kood be your Requiem (like for Mozart??). Slo-mo's of ballz rebounding from pool cushionz are terryfying. The cushion rubber bendz up, then it kumz down again az it spits the ball back out -- how can one uze Newton for spitting??? And web articles on Tangential Coefficient of Restitution etc miss by a mile. But i hav som thorts on TCOR that i can share if u head down that track. madMac. </div></div>Mac, Thanks for the warnings. I think Newtonian spitting might be an interesting challenge. /forums/images/%%GRAEMLIN_URL%%/wink.gif Also, separating friction effects from rail throwback (tangential COR), and modeling the speed effects, will be even greater challenges. That's why I wouldn't even dare attempting physics-based modeling without doing exhaustive empirical (experimental) work first. Regards,Dave</div></div>Dr Dave -- I remember (0.5)madMac years ago. I woz very happy with one test(s) i did where i mezured the angle & drop and angle and rize of a ball on a pendulum bouncing (centrally) off the vertical face of an english cushion. This looked into the most basic stuff possible for the action(s) of cushions, and (sort of) confirmed math theory. Plus (the same test really) from different hts square to the face, to check simple COR v's speed. But theze tests would be diffikult with K55 etc cushions, koz of the knife edge.

How about another test (which woz a fizzer). (0.6)madMac uzing a sharpened 10" steel nail (hanging on double-Vee pendulums, like a Roman battering ram) checking the COR response of the rubber when attacked at varyus angles. This woz meant to giv some insight into the varyation in response (ie natural vibration) of rubber cushions in the xx and yy and zz planes.

Yes, i think that the tangential COR bizness iz mainly due to extra hysteresis effekt, ie due to the rubber in the trailing edge not being able to giv back much of its force (energy) koz the ball iz saying "goodbye". I dont beleev in "build-up" ahead of a ball, but i suspekt that there might be a sort of xx komponent of rebound shortening the angle (but not on an english cushion, cloth iz too slippery and there iz too little penetration).

Bed-reaction and bed-friktion and cushion-slippage and spitting and jumping will be a nightmare. I would firstly do tests on, and model, a simple plain vertical cushion, and not introduce any funny-bizness untill later.(1.0)madmac.

dr_dave
09-11-2008, 09:55 AM
Mac,

Thank you for your "thorts." /forums/images/%%GRAEMLIN_URL%%/wink.gif

Dave

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cushioncrawler</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cushioncrawler</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dr_dave</div><div class="ubbcode-body">Bob and I hope to do a lot more experiments on kick and bank effects in the future. I also hope to try to model all of the physics effects, but I know this will be a very difficult job. There are many physical effects that control the immediate rebound angle and the amount of masse curving after rebound. I use the phrase "rail throwback" to refer to the effect you are describing. With more speed the cushion deforms more and can generate more sideways force to shorten the angle. However, the rebound angle is also affected by the efficiency (coeficient of restitution = COR) of the cushion, and this can vary with speed and angle also. Based on the results in HSV B.41 (http://billiards.colostate.edu/high_speed_videos/new/HSVB-41.htm), I think these two effects are balancing each other out. The rail throwback effect tries to shorten the rebound angle and the efficiency effect apparently tries to lengthen the rebound (because the cushion is returning less energy, maybe partly because of the ball shift down the rail). This is all conjecture, but I think it makes sense physically. I have been interested in investigating this stuff for a long time, but I want to do all of the experiments first. Regards, Dave</div></div>Dr Dave -- Dont go there -- Its impossible -- Insanity lurks there -- It kood be your Requiem (like for Mozart??). Slo-mo's of ballz rebounding from pool cushionz are terryfying. The cushion rubber bendz up, then it kumz down again az it spits the ball back out -- how can one uze Newton for spitting??? And web articles on Tangential Coefficient of Restitution etc miss by a mile. But i hav som thorts on TCOR that i can share if u head down that track. madMac. </div></div>Mac, Thanks for the warnings. I think Newtonian spitting might be an interesting challenge. /forums/images/%%GRAEMLIN_URL%%/wink.gif Also, separating friction effects from rail throwback (tangential COR), and modeling the speed effects, will be even greater challenges. That's why I wouldn't even dare attempting physics-based modeling without doing exhaustive empirical (experimental) work first. Regards,Dave</div></div>Dr Dave -- I remember (0.5)madMac years ago. I woz very happy with one test(s) i did where i mezured the angle & drop and angle and rize of a ball on a pendulum bouncing (centrally) off the vertical face of an english cushion. This looked into the most basic stuff possible for the action(s) of cushions, and (sort of) confirmed math theory. Plus (the same test really) from different hts square to the face, to check simple COR v's speed. But theze tests would be diffikult with K55 etc cushions, koz of the knife edge.

How about another test (which woz a fizzer). (0.6)madMac uzing a sharpened 10" steel nail (hanging on double-Vee pendulums, like a Roman battering ram) checking the COR response of the rubber when attacked at varyus angles. This woz meant to giv some insight into the varyation in response (ie natural vibration) of rubber cushions in the xx and yy and zz planes.

Yes, i think that the tangential COR bizness iz mainly due to extra hysteresis effekt, ie due to the rubber in the trailing edge not being able to giv back much of its force (energy) koz the ball iz saying "goodbye". I dont beleev in "build-up" ahead of a ball, but i suspekt that there might be a sort of xx komponent of rebound shortening the angle (but not on an english cushion, cloth iz too slippery and there iz too little penetration).

Bed-reaction and bed-friktion and cushion-slippage and spitting and jumping will be a nightmare. I would firstly do tests on, and model, a simple plain vertical cushion, and not introduce any funny-bizness untill later.(1.0)madmac. </div></div>